Donald Trump is the man to beat at Thursday’s GOP debate, where the Republican presidential candidates trailing him in the polls will attempt to outmaneuver the billionaire’s rhetorical body-slams.

Much of the focus has been on Trump’s hard line on immigration, with other 2016 candidates divided as to whether “The Apprentice” star has carried the party too far to the extremes. However, on a variety of other policy positions, Trump has shown himself to be at odds with the...